Biomedical subjects
Publications and source records attributed to C J Goodacre.
Since their introduction in 1973, the use of palladium-silver alloys has increased significantly and they now comprise a substantial part of the noble metal ceramic alloy sales in North America. Literature regarding various properties of this alloy system is presented with particular emphasis on castability, fit, and porcelain discoloration.
Four resin materials used to veneer metal castings were compared by evaluating certain physical properties. Three of the materials were microfilled resins and one was an unfilled resin. Although no material proved to be superior in all of the tests, the microfilled materials were generally better than the unfilled materials. The heat- and pressure- polymerized microfilled material was inferior to the two light-polymerized microfilled materials in three of the physical property tests, superior to them in one test, and proved to be equivalent to them in two tests.
As the survival rate of patients with cardiac transplants improves, it is more likely that dentists will have to provide extensive dental care and it is important to know the special precautions that must be taken when treating these patients. In this report on the prosthodontic treatment of a patient with a cardiac transplant and an unstable medical history, specific dental management guidelines are proposed. The treatment illustrates an alternative to complex and prolonged restorative treatment for patients with compromised post-transplant recovery.
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This research quantitatively compared the retention and resistance of various designs of maxillary premolar partial veneer crown preparations. Crowns were evaluated with and without proximal boxes and occlusal pins. In the absence of boxes or grooves, pins markedly enhanced both retention and resistance. In the presence of proximal boxes, pins contributed only to retention and had no significant effect on resistance. If pins are used, the cement should be spiralled into the pin hole. As resistance is usually the more crucial parameter in preparation designs, it seems that wherever efficient axial modifications can be incorporated, the pinhole modification may be of little advantage.
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Explore the source record for details and available documents.
The purpose of this study was to evaluate the procedures involved in forming high- and low-fusing solder joints between two different base metal alloys and to compare the strength of these joints with the strength of those formed between specimens made from a high-gold content alloy. The conclusions of this investigation can be summarized as follows. All but 11 of the 120 specimens failed through the solder joint, which confirms that the solder joint is usually the weakest part of a fixed partial denture. The high-fusing joints formed between the base metal alloys showed higher relative bending strength values than the high-fusing joints formed between the gold alloy specimens. The low-fusing joints formed between the base metal alloys showed higher relative bending strength values than the low-fusing joints formed between the gold alloy specimens, and the low-fusing base metal joints exhibited the highest strength values in this study. The low-fusing joints formed between gold alloy specimens consistently bent before fracturing. Solder joints fail both adhesively (separation of the solder from the parent metal) and cohesively (fracture through the solder, parent metal, or a combination of both). A correctly formed joint between gold components should show cohesive fracture, whereas adhesive fractures are apparently acceptable with base metal alloys since the low-fusing base metal joints failed in this manner but still exhibited high strength values. Voids of different sizes and locations were observed in most of the solder joints, and within each group tested there was usually less strength exhibited by the joints with larger areas of porosity.
The purpose of this study was to evaluate and compare the strength of aluminous porcelain jacket crowns made in the following manners: (1) the conventional technique, (2) the conventional technique with a pure alumina insert, (3) the twin foil technique, and (4) the twin foil technique with a pure alumina insert. The conclusions of this investigation can be summarized as follows: 1. Porosity was observed in all the restorations made by each of the techniques. 2. The porosity was greater at the porcelain-platinum foil interface than anywhere else throughout the restoration with both the conventional and twin foil techniques. 3. The porosity seemed to be evenly distributed along the interface, with no concentration in any area. 4. Regardless of the technique, crowns that were more porous fractured at lower values. 5. Crowns built by the twin foil technique were significantly more porous at the interface of the tin-plated platinum and the porcelain core than those built by the conventional technique. 6. Crowns constructed with the conventional technique were significantly stronger than those constructed with the twin foil technique. 7. There was no bond between the core porcelain and the platinum foil matrix in crowns constructed by the conventional technique. 8. There seemed to be a strong bond between the core porcelain and the tin-plated platinum matrix in crowns built by the twin foil technique. 9. The presence or absence of the alumina insert on crowns constructed with the conventional and twin foil technique did not affect the strength of the crowns when tested at the incisal edge.
A test was designed for evaluating the distintegration of cementing agents in the oral cavity. The cements were placed in small holes located in the proximal surfaces of cast gold restorations so that the materials were not subject to abrasion. Each cement was placed in one hole located occlusally and one located gingivally. Four commercial cements of four different types (zinc phosphate, zinc silicophosphate, polycarboxylate, and EBA-Alumina zinc oxide/eugenol) were tested in 15 patients, and differences were observed in the deterioration rates of the different cements over the 6 month period. The disintegration rate of a given cement was the same in the gingival and occlusal positions. No correlation was observed between the clinical data on loss of material and the solubility of the cements as measured by conventional in vitro tests.
A technique has been developed whereby collarless metal-ceramic crowns can be fabricated by spot-welding the platinum-foil matrix to the casting after it has been contoured for porcelain application. The main advantage of this procedure over previously reported techniques is that it produces well fitted restorations while requiring a lesser degree of technical skill.
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PURPOSE: This study evaluated the marginal and internal adaptation of Procera copings using different tooth preparations. The variations comprised 4 finish line forms, 3 occlusal forms, 3 occlusocervical undulation forms to the proximal finish line, and 3 proximal auxiliary retention forms. MATERIALS AND METHODS: One hundred twenty preparations were made and copings were fabricated, cemented, embedded in an epoxy resin, sectioned, and measured at 14 sites. RESULTS: The feather-edge finish line had the highest mean external marginal opening (135 +/- 79 microns), compared with the chamfer finish line (64 +/- 38 microns), the 0.8-mm rounded shoulder (51 +/- 34 microns), and the 0.5-mm rounded shoulder (68 +/- 56 microns). All 3 forms of occlusal reduction produced comparable internal adaptation at the axial wall. Specimens with normal occlusal reduction had the best occlusal adaptation at the cusp tip but not to a statistically different degree from the exaggerated form. Variations in the vertical height of interproximal finish lines did not significantly affect marginal opening. However, proximal retentive features less than 2.5 mm wide and more than 0.5 mm deep cannot be accurately reproduced with the present Procera scanner tip. CONCLUSION: Feather-edge finish-line forms, deep retentive grooves, and deep occlusal morphology are not well reproduced using this system, but all other finish-line forms and design variations are accurately and clinically acceptably reproduced using this system.
Full-thickness periosteal flap surgery is often accompanied by potential marginal bone loss and/or soft tissue recession. This is critical, particularly for the single-unit implant-supported restoration in the anterior maxilla, where the harmony of the soft and hard tissue architecture is of paramount importance to the development of natural aesthetics and function. This article demonstrates a flapless implant surgery technique in the anterior maxilla for optimal aesthetic results. The indications and limitations of this procedure are also discussed.
Prosthodontists surveyed preferred inverted V-shaped canine cingulum ledge rest seats located at the junction of the middle and cervical thirds of the lingual surface. Most respondents indicated that they preferred a ledge depth of at least 1.0 mm and indicated that their preparations usually did not extend into dentin. When the respondents evaluated various ledge depths, the mean depth of those judged adequate was 0.74 mm, which was less than the respondent and textbook recommendations. Premolar occlusal rest seats judged adequate generally met textbook size guidelines. The mean clinical incidence of dentin exposure with cingulum ledges and occlusal rest seats was 61%, close to the 55% exposure rate found on extracted teeth. Dentin Detector Gel effectively identified clinical dentin exposure but tooth sensitivity was not a good indicator of dentin exposure. Seventy-one of the 107 rest seats studied for incidence of caries and decalcification had exposed dentin but only two of the 71 had lesions. Ten of the 107 had small enamel fractures, primarily occurring on cingulum ledges.